This invention relates to digital graphics, and more particularly to a method and apparatus for digital image segmentation.
In composing and manipulating digital images for providing special effects in movie and video clips and for a variety of other imaging and graphics applications, image objects are identified and tracked. In movies, for example, image objects are inserted or manipulated to alter a scene in a realistic manner. Objects or regions from still frames or photographs are inserted into a sequence of frames to create a realistic image sequence.
Segmentation is a technique in which an object within an image is traced so that it may be extracted. Among the earliest segmentation methods is a manual method in which an operator manually selects points along a boundary of the object to outline the image. The points then are connected to formed a closed object. For example, straight lines have been used to connect the points. The more points selected the more accurate the outline.
An active contour based segmentation process improves on the manually selected rough approximation using an energy function. The energy function is computed based on a combination of internal forces relating to curve energy and external forces related to image gradient magnitude. The active contour minimizes the energy function to approximate the object boundary in an iterative process.
In a graph searching dynamic programming method, object boundary template points are manually entered. Remaining boundary points then are computer generated using a stage-wise optimal cost function.
Advances in computing technology and algorithm efficiency has enabled so-called ‘live-wire’ segmentation processes that obey the principle of minimal user interaction. In particular these processes allow the user to view the segmented object boundary as they move a selected boundary point. Herein further advances are described to enhance the accuracy and effectiveness of initial object boundary segmentation